SCR catalyst

ABSTRACT

A copper-CHA zeolite catalyst for SCR of NO x  is disclosed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the priority benefit of U.S. ProvisionalApplication No. 61/911,048, filed Dec. 3, 2013, which is incorporatedherein by reference.

FIELD OF INVENTION

The present invention relates to catalyst comprising a transition metalcontaining zeolite having a CHA framework.

BACKGROUND

Zeolites are crystalline or quasi-crystalline aluminosilicatesconstructed of repeating SiO₄ and AlO₄ tetrahedral units. These unitsare linked together to form frameworks having regular intra-crystallinecavities and channels of molecular dimensions. Numerous types ofsynthetic zeolites have been synthesized and each has a unique frameworkbased on the specific arrangement of its tetrahedral units. Byconvention, each framework type is assigned a unique three-letter code(e.g., “CHA”) by the International Zeolite Association (IZA).

Synthetic CHA zeolites are produced using a structure directing agent(SDA), also referred to as a “template” or “templating agent”. SDAs aretypically complex organic molecules which guide or direct the molecularshape and pattern of the zeolite's framework. Generally, the SDA servesto position hydrated silica and alumina and/or as a mold around whichthe zeolite crystals form. After the crystals are formed, the SDA isremoved from the interior structure of the crystals, leaving amolecularly porous aluminosilicate cage.

Zeolites have numerous industrial applications including internalcombustion engines, gas turbines, coal-fired power plants, and the like.In one example, nitrogen oxides (NO_(x)) in the exhaust gas may becontrolled through a so-called selective catalytic reduction (SCR)process whereby NO_(x) compounds in the exhaust gas are contacted with areducing agent in the presence of a zeolite catalyst.

ZSM-5 and Beta zeolites have been studied as SCR catalysts due to theirrelatively wide temperature activity window. However, the relativelylarge pore structures of these zeolites have a number of drawbacks.First, they are susceptible to high temperature hydrothermal degradationresulting in a loss of activity. Also, large and medium pore sizes tendto adsorb hydrocarbons which are oxidized as the temperature of thecatalyst increases, thus generating a significant exotherm which canthermally damage the catalyst. This problem is particularly acute inlean-burn systems, such as vehicular diesel engines, where significantquantities of hydrocarbon can be adsorbed during cold-start. Coking byhydrocarbons presents another significant drawback of these relativelylarge and medium pore molecular sieve catalysts. In contrast, small poremolecular sieve materials, such as those having a CHA framework typecode (as defined by the International Zeolite Association), offer animprovement in that fewer hydrocarbons are able to permeate into theframework.

To promote the catalytic reaction, transition metals may be included inthe zeolite material, either as a substituted framework metal (commonlyreferred to as “metal-substituted zeolite”) or as a post-synthesis ionexchanged or impregnated metal (commonly referred to as “metal-exchangedzeolite”). As used herein, the term “post-synthesis” means subsequent tozeolite crystallization. The typical process for incorporating atransition metal into a zeolite is by cationic exchange or impregnationof metals or precursors after the molecular sieve is formed. However,these exchange and impregnation processes for incorporating metalsfrequently lead to poor uniformity of metal distribution and the smallerpores of CHA type molecular sieve materials exacerbate that problem.

So-called “one pot” synthesis procedures in which a transition metalcompound is present during synthesis of the molecular sieve frameworkvis-à-vis present as a post-synthesis ion exchanged metal. However,known one-pot processes lack sufficient control over metal loading,yield framework structures with inadequate silicon to aluminum ratios(SAR), and/or necessarily include alkali metal in the synthesis mixturewhich can poison acid sites and have a detrimental effect on thehydrothermal stability. Moreover, reported one-pot synthesis proceduresfor forming metal-containing molecular sieves have been observed toyield significant amounts, in some instances as much as 20%, ofamorphous phase, copper oxides and other impurities, which negativelyimpact the stability and activity of the catalyst.

SUMMARY

Applicants have developed a novel catalyst useful for selectivelyreducing NO in an exhaust gas. The catalyst comprises acopper-containing CHA type aluminosilicate molecular sieves having molarsilica-to-alumina ratio (SAR) of at least about 40, an atomiccopper-to-aluminum ratio of at least 1.25, and preferably is essentiallyfree of ion-exchanged copper and framework transition metal, andpreferably contains less than 1.5 weight percent copper oxide.

According to certain aspects of the invention, the copper containing CHAzeolite can be prepared via a one-pot synthesis mixture by incorporatinga metal-amine complex which serves as a first CHA framework SDA and asecond, distinct CHA framework SDA. As used herein, the terms “first”and “second” with respect to SDA are used to clarify that the two SDAsare distinct compounds, but the terms do not suggest or represent theorder or sequent of operation or addition to the synthesis reactionadmixture. The combination of two SDAs into a single reaction mixture isreferred to herein as a mixed-template and the incorporation of atransition metal into the zeolite during crystallization is referred toas one-pot synthesis. Preferably, the copper-CHA zeolite is synthesizedusing Cu-tetraethylenepentamine (Cu-TEPA) andN,N,N-dimethylethylcyclohexylammonium (DMECHA) as the first and secondSDAs, respectively. Surprisingly, it has been discovered that theaddition of very low amounts of zeolite seed crystals to the reactionmixture, particularly a reaction mixture that is free or substantiallyfree of fluorine, results in CHA zeolite with a high molarsilica-to-alumina ratio (SAR).

Accordingly, in an embodiment of the invention, provided is a catalystcomposition comprising a zeolite having a CHA framework, a molarsilica-to-alumina ratio (SAR) of at least 40, and an atomiccopper-to-aluminum ratio of at least 1.25, preferably at least 1.5, andeven more preferably at least 2.

In another embodiment of the invention, provided is a catalyst articlefor treating exhaust gas comprising a catalyst composition describedherein, wherein the catalyst composition is disposed on and/or within ahoneycomb monolith substrate.

And in yet another embodiment of the invention, provided is a method fortreating an exhaust gas comprising contacting a combustion exhaust gascontaining NO_(x) and/or NH₃ with a catalyst article described herein toselectively reduce at least a portion of the NO_(x) into N₂ and H₂Oand/or oxidize at least a portion of the NH₃.

DETAILED DESCRIPTION

In general, copper-CHA zeolites are prepared from a one-pot synthesismixture containing a source of silica, a source of alumina, a first CHAframework organic templating agent in the form of a transitionmetal-amine, a second organic CHA templating agent, and seed crystals.The transition metal-amine is used to incorporate an ionic species ofthe transition metal, such as copper, into the channels and/or cavitiesof the zeolite during crystallization. The non-framework transitionmetal incorporated into the zeolite during its synthesis is referred toherein as in-situ metal. In certain embodiments, the silica, alumina,templating agents, and seed crystals are mixed to form a reactionmixture, for example a gel, which is then heated to facilitatecrystallization. The metal-containing zeolite crystals precipitate outof the reaction mixture. These crystals are collected, washed, anddried.

As used herein, the term “CHA” refers to a CHA type framework asrecognized by the International Zeolite Association (IZA) StructureCommission and the term “CHA zeolite” means an aluminosilicate in whichthe primary crystalline phase is CHA.

Applicants have discovered that the novel synthesis method describedherein is capable of producing a high phase purity CHA zeolite, i.e.,phase purities of 95% to more than 99% (as determined by Rietveld (XRD)analysis, for example). As used herein, the term phase purity withrespect to a zeolite means the amount of a single crystalline phase ofthe zeolite (e.g., based on weight) relative to total weight of allphases (crystalline and amorphous) in the zeolite substance. Thus, whileother crystalline phases be present in the CHA zeolite, the presentzeolite comprises at least about 95 weight percent CHA as a primarycrystalline phase, preferably at least about 98 weight percent CHA, andeven more preferably at least about 99 or at least about 99.9 weightpercent CHA, wherein the weight percent CHA is provided relative to thetotal weight of the zeolite crystalline phases present in thecomposition. Existing procedures for synthesizing Cu-containing CHAmaterials typically contain at least 10 weight percent, and even 20weight percent impurities.

Applicants have also found that these copper-CHA zeolites have a smallercell volume compared to other copper containing CHA zeolites. Forexample, the present zeolite has a unit cell volume of about 2355 toabout 2375 Å³, for example about 2360 to about 2370 Å³, about 2363 toabout 2365 Å³, or about 2363.5 to about 2364.5 Å³ compared to othercopper zeolites which have a unit cell volume of about 2380 Å³ or toaluminosilicate CHA which has a unit cell volume of about 2391.6 Å³.These unit cell volumes are applicable to each of the SAR ranges andtransition metal concentration ranges described herein for the presentcopper-CHA zeolite. It is believe that property improved the catalyticperformance and/or thermal durability of the material.

Preferably, the CHA zeolite is substantially free of other crystallinephases and is not an intergrowth of two or more framework types. By“substantially free” with respect to other crystalline phases, it ismeant that the present zeolite contains at least 99 weight percent CHA.

As used herein the term “zeolite” means a synthetic aluminosilicatemolecular sieve having a framework constructed of alumina and silica(i.e., repeating SiO₄ and AlO₄ tetrahedral units), and preferably havinga molar silica-to-alumina ratio (SAR) of at least 25, for example about25 to about 150. This high SAR is achieved without the need forpost-synthesis dealumination or framework defect healing processes.Accordingly, in certain embodiments, the catalyst described herein isfree from dealumination and framework defect healing treatments,particularly post-synthesis, and such as acid treatment (e.g., aceticacid), leaching with chelating agents, or steaming (e.g., 400-650° C.steam for 8-170 hours).

The zeolites of the present invention are not silica-aluminophosphates(SAPOs) and thus do not have an appreciable amount of phosphorous intheir framework. That is, the zeolite frameworks do not have phosphorousas a regular repeating unit and/or do not have an amount of phosphorousthat would affect the basic physical and/or chemical properties of thematerial, particularly with respect to the material's capacity toselectively reduce NO_(x) over a broad temperature range. In certainembodiments, the amount of framework phosphorous is less than 0.1 weightpercent, preferably less than 0.01 or less than 0.001 weight percent,based on the total weight of the zeolite.

Zeolites, as used herein, are free or substantially free of frameworkmetals, other than aluminum. Thus, a “zeolite” is distinct from a“metal-substituted zeolite” (also referred to as “isomorphoussubstituted zeolite”), wherein the latter comprises a framework thatcontains one or more non-aluminum metals substituted into the zeolite'sframework.

Suitable silica sources include, without limitation, fumed silica,silicates, precipitated silica, colloidal silica, silica gels,dealuminated zeolites such as dealuminated zeolite Y, and siliconhydroxides and alkoxides. Silica sources resulting in a high relativeyield are preferred. Typical alumina sources also are generally knownand include aluminates, alumina, other zeolites, aluminum colloids,boehmites, pseudo-boehmites, aluminum hydroxides, aluminum salts such asaluminum sulfate and alumina chloride, aluminum hydroxides andalkoxides, alumina gels.

As a first CHA SDA, a copper-amine complex is utilized. Suitable aminecomponents for the copper-amine complex include organic amines andpolyamines which are capable of directing CHA framework formation. Apreferred amine component is tetraethylenepentamine (TEPA). Themetal-amine complex (i.e., Cu-TEPA) may be pre-formed or formed in-situin the synthesis mixture from individual metal and amine components.

A second CHA framework templating agent, other than the above-notedcopper-amine complex, is selected for directing CHA synthesis. Suitablesecond organic templating agents include those having the generalformula:[R¹R²R³N—R⁴]⁺Q⁻wherein R¹ and R² are independently selected from hydrocarbyl alkylgroups and hydroxy-substituted hydrocarbyl groups having from 1 to 3carbon atoms, provided that R¹ and R² may be joined to form anitrogen-containing heterocyclic structure, R³ is an alkyl group having2 to 4 carbon atoms and R⁴ is selected from a 4- to 8-memberedcycloalkyl group, optionally substituted by 1 to 3 alkyl groups eachhaving from 1 to 3 carbon atoms, and a 4- to 8-membered heterocyclicgroup having from 1 to 3 heteroatoms, said heterocyclic group beingoptionally substituted by 1 to 3 alkyl groups each having from 1 to 3carbon atoms and the or each heteroatom in said heterocyclic group beingselected from the group consisting of O, N, and S, or R³ and R⁴ arehydrocarbyl groups having from 1 to 3 carbon atoms joined to form anitrogen-containing heterocyclic structure; and Q⁻ is a anion. Suitablestructure directing agents include N,N,N-dimethylethylcyclohexylammonium(DMECHA), N,N,N-methyldiethylcyclohexylammonium, andN,N,N-triethylcyclohexylammonium cations. Other suitable SDAs includebenzyltrimethylammonium, tetramethylammonium and1-adamantyltrimethlylammonium (TMAda), andN,N,N-triethylcyclohexylammonium cations. In certain embodiments, thesecond SDA is DMECHA.

The second organic template is in the form of a cation and preferably isassociated with an anion which is not detrimental to the formation ofthe zeolite. Representative anions include halogen, e.g., fluoride,chloride, bromide, and iodide, hydroxide, acetate, sulfate,tetrafluoroborate, carboxylate, and the like. Hydroxide is the mostpreferred ion, particularly with respect to DMECHA. In certainembodiments, the reaction mixture and subsequent zeolite is free oressentially free of fluorine.

One-pot synthesis is conducted by combining predetermined relativeamounts of the silica source, aluminum source, transition metal-aminecomplex, the second organic templating agent, and optionally a source ofhydroxide ions such as NaOH, and seed crystals, such as CHA zeolite,under various mixing and heating regimens as will be readily apparent tothose skilled in the art. The copper-CHA zeolite can be prepared from areaction mixture having the composition shown in Table 1 (shown asweight ratios). The reaction mixture can be in the form of a solution,gel, or paste, with a gel being preferred. Silicon- andaluminum-containing reactants are expressed as SiO₂ and Al₂O₃,respectively.

TABLE 1 Typical Preferred SiO₂/Al2O₃ 10-250 15-60 OH—SiO₂ 0.1-1.0 0.2-0.7 Template 1/Template 2 1:1 to 1:20  1:3-1:1.4 Templates/SiO₂0.05-0.50 0.15-0.25 Transition metal/Template 1 0.02-5   0.1-2  H₂O/SiO₂  3-50  5-30

Reaction temperatures, mixing times and speeds, and other processparameters that are suitable for conventional CHA synthesis techniquesare also generally suitable for the present invention. Withoutlimitation, the following synthesis steps may be followed to synthesizecopper-CHA zeolites according to the present invention. An aluminumsource (e.g., Al(OEt)₃) is combined with an organic templating agent(e.g., DMECHA) in water and mixed by stirring or agitation for severalminutes (e.g., about 5-30). A silica source (e.g., SiO₂) is added andmixed for several minutes (e.g., about 30-120 minutes) until ahomogeneous mixture is formed. Then, seed crystals (e.g., chabazite), acopper source (e.g. copper sulfate) and TEPA are added to the mixtureand mixed by stirring or agitation for several minutes (e.g., about15-60 minutes). Hydrothermal crystallization is usually conducted underautogenous pressure, at a temperature of about 100 to 200° C. for aduration of several days, such about 1-20 days, a preferably about 1-3days.

In preferred synthesis methods, CHA seed crystals are added to thereaction mixture. Applicants have unexpectedly found that the additionof a small amount of seed crystals, for example less than about 1 weightpercent, such as about 0.01 to about 1, about 0.05 to about 0.5, orabout 0.01 to about 0.1 weight percent, based on the total weight of thesilica in the reaction mixture.

At the conclusion the crystallization period, the resulting solids areseparated from the remaining reaction liquid by standard mechanicalseparation techniques, such as vacuum filtration. The recovered solidsare then rinsed with deionized water, and dried at an elevatedtemperature (e.g., 75-150° C.) for several hours (e.g., about 4 to 24hours). The drying step can be performed under vacuum or at atmosphericpressure.

The dried zeolite crystals are preferably calcined, but can also be usedwithout calcination.

It will be appreciated that the foregoing sequence of steps, as well aseach of the above-mentioned periods of time and temperature values aremerely exemplary and may be varied.

In certain embodiments, a source of alkali metal, such as sodium, is notadded to the synthesis mixture. The phrase “essentially alkali-free” or“alkali-free” as it is used herein means that alkali metal is not addedto the synthesis mixture as an intentional ingredient. An “essentiallyalkali-free” or “alkali-free” catalyst as referred to herein meansgenerally that the catalyst material contains an inconsequential levelof alkali metal with regard to the intended catalytic activity. Incertain embodiments, the present zeolite contains less than about 0.1weight percent, and preferably less than about 0.01 weight percent,alkali metal such as sodium or potassium.

Applicants also discovered that the foregoing one-pot synthesisprocedure permits adjusting the copper content of the crystals based onthe composition of the starting synthesis mixture. For example, adesired Cu content can be directed by providing a predetermined relativeamount of Cu source in the synthesis mixture, without requiring postsynthesis impregnation or exchange to increase or decrease the copperloading on the material. In certain embodiments, the synthesized zeolitecontains about 0.01 to about 5 weight percent copper, for example about0.1 wt. % to about 5 wt. %, from about 0.1 to about 3 wt. %, from about0.5 to about 1.5 wt. %, about 0.1 wt. % to about 1 wt. %, and about 1wt. % to about 3 wt. %. For example, a controlled Cu loading of 0.3-5%by weight, 0.5-1.5% by weight or 0.5-1.0% by weight, for example, can beachieved without additional post-synthesis processing. In certainembodiments, the zeolite is free of post-synthesis exchanged metal,including copper.

The transition metal is catalytically active and substantially uniformlydispersed within the CHA framework. Here, a substantially uniformlydispersed transition metal means that the zeolite substance contains notmore than about 5 weight percent transition metal in the form of atransition metal oxide (e.g., CuO), also referred to herein as a freetransition metal oxide, or a soluble transition metal oxide, relative tothe total amount of that transition metal in the zeolite. For example,the present zeolite contains not more than about 5 weight percent, notmore than about 3 weight percent, not more than about 1 weight percent,and not more than about 0.1 weight percent, from example about 0.01 toabout 5 weight percent, about 0.01 to about 1.5 weight percent, or about0.1 to 1 weight percent CuO based on the total weight of copper in thezeolite material. Preferably, the transition metals are not introducedinto the reaction mixture as a metal oxide and are not present in thesynthesized zeolite crystal as a metal oxide. Applicants have found thatminimizing the concentration of CuO improves the hydrothermal durabilityand exhaust gas treatment performance of the catalyst.

Preferably, the copper-CHA zeolite contains a majority of in-situtransition metal compared to free transition metal oxides. In certainembodiments, the catalyst contains a weight ratio of free transitionmetal oxides (e.g., CuO) to in-situ transition metal (e.g. ionic Cu) ofless than about 1, less than about 0.5, less than about 0.1, or lessthan about 0.01, for example about 1 to about 0.001, about 0.5 to about0.001, about 0.1 to about 0.001, or about 0.01 to about 0.001.

Preferably, the present zeolite does not contain framework transitionmetals in an appreciable amount. Instead, the copper is present as anionic species within the interior channels and cavities of the zeoliteframework. Accordingly, the copper-containing CHA zeolite is not ametal-substituted zeolite (e.g., a zeolite having a metal substitutedinto its framework structure) and not necessarily a metal-exchangedzeolite (e.g., a zeolite that underwent a post synthesis ion exchange).In certain embodiments, the zeolite is free or essentially free ofmetals other than copper and aluminum. For example, in certainembodiments, the zeolite is free or essentially free of nickel, zinc,tin, tungsten, molybdenum, cobalt, bismuth, titanium, zirconium,antimony, manganese, magnesium, chromium, vanadium, niobium, ruthenium,rhodium, palladium, gold, silver, indium, platinum, iridium, and/orrhenium. In certain embodiments, the zeolite is free or essentially freeof iron. In certain embodiments, the zeolite is free or essentially freeof calcium. In certain embodiments, the zeolite is free or essentiallyfree of cerium.

The zeolite is useful as a catalyst in certain applications. Thecatalyst preferably is used without a post-synthesis metal exchange.However, in certain embodiments, the catalyst can undergo apost-synthesis metal exchange. Thus, in certain embodiments, provided isa catalyst comprising a CHA zeolite containing one or more catalyticmetals exchanged into the channels and/or cavities of the zeolite postzeolite-synthesis in addition to in-situ copper. Examples of metals thatcan be post-zeolite synthesis exchanged or impregnated includetransition metals, including copper, nickel, zinc, iron, tungsten,molybdenum, cobalt, titanium, zirconium, manganese, chromium, vanadium,niobium, as well as tin, bismuth, and antimony; noble metals includingplatinum group metals (PGMs), such as ruthenium, rhodium, palladium,indium, platinum, and precious metals such as gold and silver; alkalineearth metals such as beryllium, magnesium, calcium, strontium, andbarium; and rare earth metals such as lanthanum, cerium, praseodymium,neodymium, europium, terbium, erbium, ytterbium, and yttrium. Preferredtransition metals for post-synthesis exchange are base metals, andpreferred base metals include those selected from the group consistingof manganese, iron, cobalt, nickel, and mixtures thereof. Metalsincorporated post-synthesis can be added to the molecular sieve via anyknown technique such as ion exchange, impregnation, isomorphoussubstitution, etc. The amount of metal post-synthesis exchanged can befrom about 0.1 to about 3 weight percent, for example about 0.1 to about1 weight percent, based on the total weight of the zeolite.

In certain embodiments, the metal-containing zeolite containspost-synthesis exchanged alkaline earth metal, particularly calciumand/or magnesium, disposed within the channels and/or cavities of thezeolite framework. Thus, the metal-containing zeolite of the presentinvention can have transition metals (T_(M)), such as copper,incorporated into the zeolite channels and/or cavities during synthesisand have one or more exchanged alkaline earth metals (A_(M)), such ascalcium or potassium, incorporated post-synthesis. The alkaline earthmetal can be present in an amount relative to the transition metal thatis present. For example, in certain embodiments, T_(M) and A_(M) arepresent, respectively, in a molar ratio of about 15:1 to about 1:1, forexample about 10:1 to about 2:1, about 10:1 to about 3:1, or about 6:1to about 4:1, particularly were T_(M) is copper and A_(M) is calcium. Incertain embodiments, the relative cumulative amount of transition metal(T_(M)) and alkali and/or alkaline earth metal (A_(M)) is present in thezeolite material in an amount relative to the amount of aluminum in thezeolite, namely the framework aluminum. As used herein, the(T_(M)+A_(M)):Al ratio is based on the relative molar amounts ofT_(M)+A_(M) to molar framework Al in the corresponding zeolite. Incertain embodiments, the catalyst material has a (T_(M)+A_(M)):Al ratioof not more than about 0.6. In certain embodiments, the (T_(M)+A_(M)):Alratio is not more than 0.5, for example about 0.05 to about 0.5, about0.1 to about 0.4, or about 0.1 to about 0.2.

In certain embodiments, Ce is post-synthesis impregnated into thecatalyst, for example by adding Ce nitrate to a copper promoted zeolitevia a conventional incipient wetness technique. Preferably, the ceriumconcentration in the catalyst material is present in a concentration ofat least about 1 weight percent, based on the total weight of thezeolite. Examples of preferred concentrations include at least about 2.5weight percent, at least about 5 weight percent, at least about 8 weightpercent, at least about 10 weight percent, about 1.35 to about 13.5weight percent, about 2.7 to about 13.5 weight percent, about 2.7 toabout 8.1 weight percent, about 2 to about 4 weight percent, about 2 toabout 9.5 weight percent, and about 5 to about 9.5 weight percent, basedon the total weight of the zeolite. In certain embodiments, the ceriumconcentration in the catalyst material is about 50 to about 550 g/ft³.Other ranges of Ce include: above 100 g/ft³, above 200 g/ft³, above 300g/ft³, above 400 g/ft³, above 500 g/ft³, from about 75 to about 350g/ft³, from about 100 to about 300 g/ft³, and from about 100 to about250 g/ft³.

For embodiments in which the catalyst is part of a washcoat composition,the washcoat may further comprise binder containing Ce or ceria. Forsuch embodiments, the Ce containing particles in the binder aresignificantly larger than the Ce containing particles in the catalyst.

Applicants further discovered that the foregoing one-pot synthesisprocedure permits adjusting the SAR of the catalyst based on thecomposition of the starting synthesis mixture. SARs of 40-250, 40-150,40-100, 40-80, and 40-50, for example, can be selectively achieved basedon the composition of the starting synthesis mixture and/or adjustingother process variables. The SAR of zeolites may be determined byconventional analysis. This ratio is meant to represent, as closely aspossible, the ratio in the rigid atomic framework of the zeolite crystaland to exclude silicon or aluminum in the binder or, in cationic orother form, within the channels. It will be appreciated that it may beextremely difficult to directly measure the SAR of zeolite after it hasbeen combined with a binder material. Accordingly, the SAR has beenexpressed hereinabove in term of the SAR of the parent zeolite, i.e.,the zeolite used to prepare the catalyst, as measured prior to thecombination of this zeolite with the other catalyst components.

The foregoing one-pot synthesis procedure can result in zeolite crystalsof uniform size and shape with relatively low amounts of agglomeration.In addition, the synthesis procedure can result in zeolite crystalshaving a mean crystalline size of about 0.1 to about 10 μm, for exampleabout 0.5 to about 5 μm, about 0.1 to about 1 μm, about 1 to about 5 μm,about 3 to about 7 μm, and the like. In certain embodiments, largecrystals are milled using a jet mill or other particle-on-particlemilling technique to an average size of about 1.0 to about 1.5 micron tofacilitate washcoating a slurry containing the catalyst to a substrate,such as a flow-through monolith.

Crystal size is the length of one edge of a face of the crystal. Directmeasurement of the crystal size can be performed using microscopymethods, such as SEM and TEM. Other techniques for determining meanparticle size, such as laser diffraction and scattering can also beused. In addition to the mean crystal size, catalyst compositionspreferably have a majority of the crystal sizes are greater than about0.1 μm, preferably between about 0.5 and about 5 μm, such as about 0.5to about 5 μm, about 0.7 to about 5 μm, about 1 to about 5 μm, about 1.5to about 5.0 μm, about 1.5 to about 4.0 μm, about 2 to about 5 μm, orabout 1 μm to about 10 μm.

Catalysts of the present invention are particularly applicable forheterogeneous catalytic reaction systems (i.e., solid catalyst incontact with a gas reactant). To improve contact surface area,mechanical stability, and/or fluid flow characteristics, the catalystscan be disposed on and/or within a substrate, preferably a poroussubstrate. In certain embodiments, a washcoat containing the catalyst isapplied to an inert substrate, such as corrugated metal plate or ahoneycomb cordierite brick. Alternatively, the catalyst is kneaded alongwith other components such as fillers, binders, and reinforcing agents,into an extrudable paste which is then extruded through a die to form ahoneycomb brick. Accordingly, in certain embodiments provided is acatalyst article comprising a copper-CHA zeolite catalyst describedherein coated on and/or incorporated into a substrate.

Certain aspects of the invention provide a catalytic washcoat. Thewashcoat comprising the copper-CHA zeolite catalyst described herein ispreferably a solution, suspension, or slurry. Suitable coatings includesurface coatings, coatings that penetrate a portion of the substrate,coatings that permeate the substrate, or some combination thereof.

A washcoat can also include non-catalytic components, such as fillers,binders, stabilizers, rheology modifiers, and other additives, includingone or more of alumina, silica, non-zeolite silica alumina, titania,zirconia, ceria. In certain embodiments, the catalyst composition maycomprise pore-forming agents such as graphite, cellulose, starch,polyacrylate, and polyethylene, and the like. These additionalcomponents do not necessarily catalyze the desired reaction, but insteadimprove the catalytic material's effectiveness, for example, byincreasing its operating temperature range, increasing contact surfacearea of the catalyst, increasing adherence of the catalyst to asubstrate, etc. In preferred embodiments, the washcoat loading is >0.3g/in³, such as >1.2 g/in³, >1.5 g/in³, >1.7 g/in³ or >2.00 g/in³, andpreferably <3.5 g/in³, such as <2.5 g/in³. In certain embodiments, thewashcoat is applied to a substrate in a loading of about 0.8 to 1.0g/in³, 1.0 to 1.5 g/in³, or 1.5 to 2.5 g/in³.

Two of the most common substrate designs are plate and honeycomb.Preferred substrates, particularly for mobile applications, includeflow-through monoliths having a so-called honeycomb geometry thatcomprise multiple adjacent, parallel channels that are open on both endsand generally extend from the inlet face to the outlet face of thesubstrate and result in a high-surface area-to-volume ratio. For certainapplications, the honeycomb flow-through monolith preferably has a highcell density, for example about 600 to 800 cells per square inch, and/oran average internal wall thickness of about 0.18-0.35 mm, preferablyabout 0.20-0.25 mm. For certain other applications, the honeycombflow-through monolith preferably has a low cell density of about 150-600cells per square inch, more preferably about 200-400 cells per squareinch. Preferably, the honeycomb monoliths are porous. In addition tocordierite, silicon carbide, silicon nitride, ceramic, and metal, othermaterials that can be used for the substrate include aluminum nitride,silicon nitride, aluminum titanate, α-alumina, mullite, e.g., acicularmullite, pollucite, a thermet such as Al₂OsZFe, Al₂O₃/Ni or B₄CZFe, orcomposites comprising segments of any two or more thereof. Preferredmaterials include cordierite, silicon carbide, and alumina titanate.

Plate-type catalysts have lower pressure drops and are less susceptibleto plugging and fouling than the honeycomb types, which is advantageousin high efficiency stationary applications, but plate configurations canbe much larger and more expensive. A honeycomb configuration istypically smaller than a plate type, which is an advantage in mobileapplications, but has higher pressure drops and plug more easily. Incertain embodiments the plate substrate is constructed of metal,preferably corrugated metal.

In certain embodiments, the invention is a catalyst article made by aprocess described herein. In a particular embodiment, the catalystarticle is produced by a process that includes the steps of applying thecatalyst composition, preferably as a washcoat, to a substrate as alayer either before or after at least one additional layer of anothercomposition for treating exhaust gas has been applied to the substrate.The one or more catalyst layers on the substrate, including the presentcatalyst layer, are arranged in consecutive layers. As used herein, theterm “consecutive” with respect to catalyst layers on a substrate meansthat each layer is contact with its adjacent layer(s) and that thecatalyst layers as a whole are arranged one on top of another on thesubstrate.

In certain embodiments, the present catalyst is disposed on thesubstrate as a first layer and another composition, such as an oxidationcatalyst, reduction catalyst, scavenging component, or NO_(x) storagecomponent, is disposed on the substrate as a second layer. In otherembodiments, the present catalyst is disposed on the substrate as asecond layer and another composition, such as such as an oxidationcatalyst, reduction catalyst, scavenging component, or NO_(x) storagecomponent, is disposed on the substrate as a first layer. As used hereinthe terms “first layer” and “second layer” are used to describe therelative positions of catalyst layers in the catalyst article withrespect to the normal direction of exhaust gas flow-through, past,and/or over the catalyst article. Under normal exhaust gas flowconditions, exhaust gas contacts the first layer prior to contacting thesecond layer. In certain embodiments, the second layer is applied to aninert substrate as a bottom layer and the first layer is top layer thatis applied over the second layer as a consecutive series of sub-layers.In such embodiments, the exhaust gas penetrates (and hence contacts) thefirst layer, before contacting the second layer, and subsequentlyreturns through the first layer to exit the catalyst component. In otherembodiments, the first layer is a first zone disposed on an upstreamportion of the substrate and the second layer is disposed on thesubstrate as a second zone, wherein the second zone is downstream of thefirst.

In another embodiment, the catalyst article is produced by a processthat includes the steps of applying the present catalyst composition,preferably as a washcoat, to a substrate as a first zone, andsubsequently applying at least one additional composition for treatingan exhaust gas to the substrate as a second zone, wherein at least aportion of the first zone is downstream of the second zone.Alternatively, the present catalyst composition can be applied to thesubstrate in a second zone that is downstream of a first zone containingthe additional composition. Examples of additional compositions includeoxidation catalysts, reduction catalysts, scavenging components (e.g.,for sulfur, water, etc.), or NO_(x) storage components.

To reduce the amount of space required for an exhaust system, individualexhaust components in certain embodiments are designed to perform morethan one function. For example, applying an SCR catalyst to a wall-flowfilter substrate instead of a flow-through substrate serves to reducethe overall size of an exhaust treatment system by allowing onesubstrate to serve two functions, namely catalytically reducing NO_(x)concentration in the exhaust gas and mechanically removing soot from theexhaust gas. Accordingly, in certain embodiments, the substrate is ahoneycomb wall-flow filter or partial filter. Wall-flow filters aresimilar to flow-through honeycomb substrates in that they contain aplurality of adjacent, parallel channels. However, the channels offlow-through honeycomb substrates are open at both ends, whereas thechannels of wall-flow substrates have one end capped, wherein thecapping occurs on opposite ends of adjacent channels in an alternatingpattern. Capping alternating ends of channels prevents the gas enteringthe inlet face of the substrate from flowing straight through thechannel and existing. Instead, the exhaust gas enters the front of thesubstrate and travels into about half of the channels where it is forcedthrough the channel walls prior to entering the second half of thechannels and exiting the back face of the substrate.

The substrate wall has a porosity and pore size that is gas permeable,but traps a major portion of the particulate matter, such as soot, fromthe gas as the gas passes through the wall. Preferred wall-flowsubstrates are high efficiency filters. Wall flow filters for use withthe present invention preferably have an efficiency of least 70%, atleast about 75%, at least about 80%, or at least about 90%. In certainembodiments, the efficiency will be from about 75 to about 99%, about 75to about 90%, about 80 to about 90%, or about 85 to about 95%. Here,efficiency is relative to soot and other similarly sized particles andto particulate concentrations typically found in conventional dieselexhaust gas. For example, particulates in diesel exhaust can range insize from 0.05 microns to 2.5 microns. Thus, the efficiency can be basedon this range or a sub-range, such as 0.1 to 0.25 microns, 0.25 to 1.25microns, or 1.25 to 2.5 microns.

Porosity is a measure of the percentage of void space in a poroussubstrate and is related to backpressure in an exhaust system:generally, the lower the porosity, the higher the backpressure.Preferably, the porous substrate has a porosity of about 30 to about80%, for example about 40 to about 75%, about 40 to about 65%, or fromabout 50 to about 60%.

The pore interconnectivity, measured as a percentage of the substrate'stotal void volume, is the degree to which pores, void, and/or channels,are joined to form continuous paths through a porous substrate, i.e.,from the inlet face to the outlet face. In contrast to poreinterconnectivity is the sum of closed pore volume and the volume ofpores that have a conduit to only one of the surfaces of the substrate.Preferably, the porous substrate has a pore interconnectivity volume ofat least about 30%, more preferably at least about 40%.

The mean pore size of the porous substrate is also important forfiltration. Mean pore size can be determined by any acceptable means,including by mercury porosimetry. The mean pore size of the poroussubstrate should be of a high enough value to promote low backpressure,while providing an adequate efficiency by either the substrate per se,by promotion of a soot cake layer on the surface of the substrate, orcombination of both. Preferred porous substrates have a mean pore sizeof about 10 to about 40 μm, for example about 20 to about 30 μm, about10 to about 25 μm, about 10 to about 20 μm, about 20 to about 25 μm,about 10 to about 15 μm, and about 15 to about 20 μm.

In general, the production of an extruded solid body containing thecopper-CHA zeolite catalyst involves blending the catalyst, a binder, anoptional organic viscosity-enhancing compound into an homogeneous pastewhich is then added to a binder/matrix component or a precursor thereofand optionally one or more of stabilized ceria, and inorganic fibers.The blend is compacted in a mixing or kneading apparatus or an extruder.The mixtures have organic additives such as binders, pore formers,plasticizers, surfactants, lubricants, dispersants as processing aids toenhance wetting and therefore produce a uniform batch. The resultingplastic material is then molded, in particular using an extrusion pressor an extruder including an extrusion die, and the resulting moldingsare dried and calcined. The organic additives are “burnt out” duringcalcinations of the extruded solid body. The copper-CHA zeolite catalystmay also be washcoated or otherwise applied to the extruded solid bodyas one or more sub-layers that reside on the surface or penetrate whollyor partly into the extruded solid body.

Extruded solid bodies containing the catalysts according to the presentinvention generally comprise a unitary structure in the form of ahoneycomb having uniform-sized and parallel channels extending from afirst end to a second end thereof. Channel walls defining the channelsare porous. Typically, an external “skin” surrounds a plurality of thechannels of the extruded solid body. The extruded solid body can beformed from any desired cross section, such as circular, square or oval.Individual channels in the plurality of channels can be square,triangular, hexagonal, circular etc. Channels at a first, upstream endcan be blocked, e.g. with a suitable ceramic cement, and channels notblocked at the first, upstream end can also be blocked at a second,downstream end to form a wall-flow filter. Typically, the arrangement ofthe blocked channels at the first, upstream end resembles achecker-board with a similar arrangement of blocked and open downstreamchannel ends.

The binder/matrix component is preferably selected from the groupconsisting of cordierite, nitrides, carbides, borides, intermetallics,lithium aluminosilicate, a spinel, an optionally doped alumina, a silicasource, titania, zirconia, titania-zirconia, zircon and mixtures of anytwo or more thereof. The paste can optionally contain reinforcinginorganic fibers selected from the group consisting of carbon fibers,glass fibers, metal fibers, boron fibers, alumina fibers, silica fibers,silica-alumina fibers, silicon carbide fibers, potassium titanatefibers, aluminum borate fibers and ceramic fibers.

The alumina binder/matrix component is preferably gamma alumina, but canbe any other transition alumina, i.e., alpha alumina, beta alumina, chialumina, eta alumina, rho alumina, kappa alumina, theta alumina, deltaalumina, lanthanum beta alumina and mixtures of any two or more suchtransition aluminas. It is preferred that the alumina is doped with atleast one non-aluminum element to increase the thermal stability of thealumina. Suitable alumina dopants include silicon, zirconium, barium,lanthanides and mixtures of any two or more thereof. Suitable lanthanidedopants include La, Ce, Nd, Pr, Gd and mixtures of any two or morethereof.

Sources of silica can include a silica sol, quartz, fused or amorphoussilica, sodium silicate, an amorphous aluminosilicate, an alkoxysilane,a silicone resin binder such as methylphenyl silicone resin, a clay,talc or a mixture of any two or more thereof. Of this list, the silicacan be SiO₂ as such, feldspar, mullite, silica-alumina, silica-magnesia,silica-zirconia, silica-thoria, silica-berylia, silica-titania, ternarysilica-alumina-zirconia, ternary silica-alumina-magnesia,ternary-silica-magnesia-zirconia, ternary silica-alumina-thoria andmixtures of any two or more thereof.

Preferably, the copper-CHA zeolite catalyst is dispersed throughout, andpreferably evenly throughout, the entire extruded catalyst body.

Where any of the above extruded solid bodies are made into a wall-flowfilter, the porosity of the wall-flow filter can be from 30-80%, such asfrom 40-70%. Porosity and pore volume and pore radius can be measurede.g. using mercury intrusion porosimetry.

The catalyst described herein can promote the reaction of a reductant,preferably ammonia, with nitrogen oxides to selectively form elementalnitrogen (N₂) and water (H₂O). Thus, in one embodiment, the catalyst canbe formulated to favor the reduction of nitrogen oxides with a reductant(i.e., an SCR catalyst). Examples of such reductants includehydrocarbons (e.g., C3-C6 hydrocarbons) and nitrogenous reductants suchas ammonia and ammonia hydrazine or any suitable ammonia precursor, suchas urea ((NH₂)₂CO), ammonium carbonate, ammonium carbamate, ammoniumhydrogen carbonate or ammonium formate.

The copper-CHA zeolite catalyst described herein can also promote theoxidation of ammonia. Thus, in another embodiment, the catalyst can beformulated to favor the oxidation of ammonia with oxygen, particularly aconcentrations of ammonia typically encountered downstream of an SCRcatalyst (e.g., ammonia oxidation (AMOX) catalyst, such as an ammoniaslip catalyst (ASC)). In certain embodiments, the present catalyst isdisposed as a top layer over an oxidative under-layer, wherein theunder-layer comprises a platinum group metal (PGM) catalyst or a non-PGMcatalyst. Preferably, the catalyst component in the underlayer isdisposed on a high surface area support, including but not limited toalumina.

In yet another embodiment, an SCR and AMOX operations are performed inseries, wherein both processes utilize a catalyst comprising thecopper-CHA zeolite catalyst described herein, and wherein the SCRprocess occurs upstream of the AMOX process. For example, an SCRformulation of the catalyst can be disposed on the inlet side of afilter and an AMOX formulation of the catalyst can be disposed on theoutlet side of the filter.

Accordingly, provided is a method for the reduction of NO_(x) compoundsor oxidation of NH₃ in a gas, which comprises contacting the gas with acatalyst composition described herein for the catalytic reduction ofNO_(x) compounds for a time sufficient to reduce the level of NO_(x)compounds and/or NH₃ in the gas. In certain embodiments, provided is acatalyst article having an ammonia slip catalyst disposed downstream ofa selective catalytic reduction (SCR) catalyst. In such embodiments, theammonia slip catalyst oxidizes at least a portion of any nitrogenousreductant that is not consumed by the selective catalytic reductionprocess. For example, in certain embodiments, the ammonia slip catalystis disposed on the outlet side of a wall flow filter and an SCR catalystis disposed on the upstream side of a filter. In certain otherembodiments, the ammonia slip catalyst is disposed on the downstream endof a flow-through substrate and an SCR catalyst is disposed on theupstream end of the flow-through substrate. In other embodiments, theammonia slip catalyst and SCR catalyst are disposed on separate brickswithin the exhaust system. These separate bricks can be adjacent to, andin contact with, each other or separated by a specific distance,provided that they are in fluid communication with each other andprovided that the SCR catalyst brick is disposed upstream of the ammoniaslip catalyst brick.

In certain embodiments, the SCR and/or AMOX process is performed at atemperature of at least 100° C. In another embodiment, the process(es)occur at a temperature from about 150° C. to about 750° C. In aparticular embodiment, the temperature range is from about 175 to about550° C. In another embodiment, the temperature range is from 175 to 400°C. In yet another embodiment, the temperature range is 450 to 900° C.,preferably 500 to 750° C., 500 to 650° C., 450 to 550° C., or 650 to850° C. Embodiments utilizing temperatures greater than 450° C. areparticularly useful for treating exhaust gases from a heavy and lightduty diesel engine that is equipped with an exhaust system comprising(optionally catalyzed) diesel particulate filters which are regeneratedactively, e.g. by injecting hydrocarbon into the exhaust system upstreamof the filter, wherein the zeolite catalyst for use in the presentinvention is located downstream of the filter.

According to another aspect of the invention, provided is a method forthe reduction of NO_(x) compounds and/or oxidation of NH₃ in a gas,which comprises contacting the gas with a catalyst described herein fora time sufficient to reduce the level of NO_(x) compounds in the gas.Methods of the present invention may comprise one or more of thefollowing steps: (a) accumulating and/or combusting soot that is incontact with the inlet of a catalytic filter; (b) introducing anitrogenous reducing agent into the exhaust gas stream prior tocontacting the catalytic filter, preferably with no interveningcatalytic steps involving the treatment of NO_(x) and the reductant; (c)generating NH₃ over a NO_(x) adsorber catalyst or lean NO_(x) trap, andpreferably using such NH₃ as a reductant in a downstream SCR reaction;(d) contacting the exhaust gas stream with a DOC to oxidize hydrocarbonbased soluble organic fraction (SOF) and/or carbon monoxide into CO₂,and/or oxidize NO into NO₂, which in turn, may be used to oxidizeparticulate matter in particulate filter; and/or reduce the particulatematter (PM) in the exhaust gas; (e) contacting the exhaust gas with oneor more flow-through SCR catalyst device(s) in the presence of areducing agent to reduce the NOx concentration in the exhaust gas; and(f) contacting the exhaust gas with an ammonia slip catalyst, preferablydownstream of the SCR catalyst to oxidize most, if not all, of theammonia prior to emitting the exhaust gas into the atmosphere or passingthe exhaust gas through a recirculation loop prior to exhaust gasentering/re-entering the engine.

In another embodiment, all or at least a portion of the nitrogen-basedreductant, particularly NH₃, for consumption in the SCR process can besupplied by a NO_(x) adsorber catalyst (NAC), a lean NO_(x) trap (LNT),or a NO_(x) storage/reduction catalyst (NSRC), disposed upstream of theSCR catalyst, e.g., a SCR catalyst of the present invention disposed ona wall-flow filter. NAC components useful in the present inventioninclude a catalyst combination of a basic material (such as alkalimetal, alkaline earth metal or a rare earth metal, including oxides ofalkali metals, oxides of alkaline earth metals, and combinationsthereof), and a precious metal (such as platinum), and optionally areduction catalyst component, such as rhodium. Specific types of basicmaterial useful in the NAC include cesium oxide, potassium oxide,magnesium oxide, sodium oxide, calcium oxide, strontium oxide, bariumoxide, and combinations thereof. The precious metal is preferablypresent at about 10 to about 200 g/ft³, such as 20 to 60 g/ft³.Alternatively, the precious metal of the catalyst is characterized bythe average concentration which may be from about 40 to about 100grams/ft³.

Under certain conditions, during the periodically rich regenerationevents, NH₃ may be generated over a NO_(x) adsorber catalyst. The SCRcatalyst downstream of the NO_(x) adsorber catalyst may improve theoverall system NO_(x) reduction efficiency. In the combined system, theSCR catalyst is capable of storing the released NH₃ from the NACcatalyst during rich regeneration events and utilizes the stored NH₃ toselectively reduce some or all of the NO_(x) that slips through the NACcatalyst during the normal lean operation conditions.

The method for treating exhaust gas as described herein can be performedon an exhaust gas derived from a combustion process, such as from aninternal combustion engine (whether mobile or stationary), a gas turbineand coal or oil fired power plants. The method may also be used to treatgas from industrial processes such as refining, from refinery heatersand boilers, furnaces, the chemical processing industry, coke ovens,municipal waste plants and incinerators, etc. In a particularembodiment, the method is used for treating exhaust gas from a vehicularlean burn internal combustion engine, such as a diesel engine, alean-burn gasoline engine or an engine powered by liquid petroleum gasor natural gas.

In certain aspects, the invention is a system for treating exhaust gasgenerated by combustion process, such as from an internal combustionengine (whether mobile or stationary), a gas turbine, coal or oil firedpower plants, and the like. Such systems include a catalytic articlecomprising the catalyst described herein and at least one additionalcomponent for treating the exhaust gas, wherein the catalytic articleand at least one additional component are designed to function as acoherent unit.

In certain embodiments, the system comprises a catalytic articlecomprising a catalyst described herein, a conduit for directing aflowing exhaust gas, a source of nitrogenous reductant disposed upstreamof the catalytic article. The system can include a controller for themetering the nitrogenous reductant into the flowing exhaust gas onlywhen it is determined that the zeolite catalyst is capable of catalyzingNO_(x) reduction at or above a desired efficiency, such as at above 100°C., above 150° C. or above 175° C. The metering of the nitrogenousreductant can be arranged such that 60% to 200% of theoretical ammoniais present in exhaust gas entering the SCR catalyst calculated at 1:1NH₃/NO and 4:3 NH₃/NO₂.

In another embodiment, the system comprises an oxidation catalyst (e.g.,a diesel oxidation catalyst (DOC)) for oxidizing nitrogen monoxide inthe exhaust gas to nitrogen dioxide can be located upstream of a pointof metering the nitrogenous reductant into the exhaust gas. In oneembodiment, the oxidation catalyst is adapted to yield a gas streamentering the SCR zeolite catalyst having a ratio of NO to NO₂ of fromabout 4:1 to about 1:3 by volume, e.g. at an exhaust gas temperature atoxidation catalyst inlet of 250° C. to 450° C. The oxidation catalystcan include at least one platinum group metal (or some combination ofthese), such as platinum, palladium, or rhodium, coated on aflow-through monolith substrate. In one embodiment, the at least oneplatinum group metal is platinum, palladium or a combination of bothplatinum and palladium. The platinum group metal can be supported on ahigh surface area washcoat component such as alumina, a zeolite such asan aluminosilicate zeolite, silica, non-zeolite silica alumina, ceria,zirconia, titania or a mixed or composite oxide containing both ceriaand zirconia.

In a further embodiment, a suitable filter substrate is located betweenthe oxidation catalyst and the SCR catalyst. Filter substrates can beselected from any of those mentioned above, e.g. wall flow filters.Where the filter is catalyzed, e.g. with an oxidation catalyst of thekind discussed above, preferably the point of metering nitrogenousreductant is located between the filter and the zeolite catalyst.Alternatively, if the filter is un-catalyzed, the means for meteringnitrogenous reductant can be located between the oxidation catalyst andthe filter.

What is claimed is:
 1. A catalyst composition comprising acopper-containing zeolite having a CHA framework, a molarsilica-to-alumina ratio (SAR) of at least 40, and an atomiccopper-to-aluminum ratio of at least 1.25, wherein the zeolite isessentially free of ion-exchanged copper and the zeolite is essentiallyfree of framework transition metal.
 2. The catalyst composition of claim1, wherein the copper-to-aluminum ratio is at least 1.5.
 3. The catalystcomposition of claim 1, wherein the copper-to-aluminum ratio of at least2.
 4. The catalyst composition of claim 1, wherein the SAR is 40 to 250.5. The catalyst composition of claim 1, wherein the SAR is about 45 to85.
 6. The catalyst composition of claim 1, copper is present in anamount of about 3 to 5 weight percent, based on the total weight of thezeolite.
 7. The catalyst composition of claim 1, wherein the zeolitecontains less than 1.5 weight percent copper oxide.
 8. A catalystarticle for treating exhaust gas comprising a catalyst compositionaccording to claim 1 disposed on and/or within a substrate.
 9. Thecatalyst article of claim 8, wherein the substrate is a metal plate. 10.The catalyst article of claim 8, wherein the substrate is a honeycomb.11. The catalyst article of claim 10, wherein the catalyst is a washcoaton the honeycomb.
 12. The catalyst article of claim 10, wherein thehoneycomb is an extruded catalyst.
 13. The catalyst article of claim 10,wherein the honeycomb is a wall-flow filter.
 14. The catalyst article ofclaim 10, wherein the honeycomb is a flow-through honeycomb.
 15. Acatalyst composition comprising a washcoat slurry comprising a catalystaccording to claim 1 and one or more binders.
 16. A method for treatingan exhaust gas comprising contacting a combustion exhaust gas containingNO_(x) and/or NH₃ with a catalyst composition according to claim 1 toselectively reduce at least a portion of the NO_(x) into N₂ and H₂Oand/or oxidize at least a portion of the NH₃.
 17. A system for treatingan exhaust gas containing NOx, the system comprising a catalytic articleaccording to claim 8 and a source of a reductant, wherein the reductantsource is upstream of the catalytic article.
 18. A catalyst compositioncomprising a copper-containing zeolite having a CHA framework, a molarsilica-to-alumina ratio (SAR) of at least 40, and an atomiccopper-to-aluminum ratio of at least 1.25, wherein the zeolite comprisesa majority of in-situ copper compared to free copper oxides.
 19. Acatalyst composition comprising a copper-containing zeolite having a CHAframework, a molar silica-to-alumina ratio (SAR) of at least 40, and anatomic copper-to-aluminum ratio of at least 1.25, wherein the zeolitehas a unit cell volume of about 2355 to about 2375 A³.